Aliminum plating process

ABSTRACT

Aluminum plating according to which aluminum film formed has no cracks and pin-holes on its surface, a uniform thickness, excellent luster and is strongly bonded to the substrate can be attained by heat treating a substrate covered with aluminum at 400* C the melting point of aluminum for 10 seconds 30 minutes in an inert atmosphere said heat treatment being preceded by or followed by treating of the covered substrate with a surface treating agent comprising active hydrogen-containing compound, oxygen or halogen and thereafter taking out thus treated substrate into the air.

United States Patent [191 Ichiki et al.

[451 Aug. 21, 1973 ALIMINUM PLATING PROCESS [73] Assignee: SumitomoChemical Company Limited, Osaka, Japan [22] Filed: Oct. 30, 1970 [2]]Appl. No.: 85,823

[30] Foreign Application Priority Data Nov. 1, 1969 Japan 44/87965 [52]US. Cl 1l7/107.2, 117/62, 117/227, 148/627 [51] Int. Cl..... C23cll/02[58] Field of Search 117/107.2, 35 V, 117/62, 227; 75/68 C, 68 R, 68 A,68 B; 148/627 [56] References Cited 1 UNITED STATES PATENTS 3,535,10810/1970 Kobetz et al 75/68 C 3,154,407 10/1964 Ikeda et al. 75/68 C2,880,115 3/1959 Drummond...... ll7/l07.2 X 2,887,984 5/1959 Drummond1l7/107.2 X 2,443,196 6/1948 Raines et al. ll7/35 V 2,843,506 7/1958Drummond 1l7/l07.2 R 2,643,959 6/1953 Fischer et al. ll7/l07.2 R

Primary Examiner-Ralph S. Kendall Attorney-Stevens, Davis, Miller andMosher 5 7] ABSTRACT Aluminum plating according to which aluminum filmformed has no cracks and pin-holes on its surface, a uniform thickness,excellent luster and is strongly bonded to the substrate can be attainedby heat treating a substrate covered with aluminum at 400 C the meltingpoint of aluminum for 10 seconds 30 minutes in an inert atmosphere saidheat treatment being preceded by or followed by treating of the coveredsubstrate with a surface treating agentcomprising activehydrogencontaining compound, oxygen or halogen and thereafter taking outthus treated substrate into the air.

38 Claims, No Drawings ALUMINUM PLATING PROCESS This invention relatesto an aluminum plating process and more particularly it concerns aprocess for effecting excellent aluminum plating on a substrate bycontacting a heated substrate with an alkyl aluminum compound to causethermal decomposition of said alkyl aluminum.

By the term a substrate covered with aluminum is meant a substrate whichhas been covered with aluminum produced by thermal decomposition of analkyl aluminum compound which is caused by contact of the heatedsubstrate with the alkyl aluminum compound, but which has not yet beentaken out into the air.

It has been proposed by K. Ziegler et al. to plate a substrate withaluminum by contacting a heated substrate with a liquid alkyl aluminumcompound or with vapor of an alkyl aluminum compound to cause thermaldecomposition of said alkyl aluminum. In this respect, see, for example,Japanese Pat. No. 234069.

However, such method for plating a substrate with aluminum provides suchserious drawbacks as mentioned below.

That is, the aluminum film plated on the substrate has cracks andpin-holes which cause deterioration of the corrosion resistance, theoxidation resistance at a high temperature and the electriccharacteristics. Furthermore, the thickness of aluminum film is notuniform, luster of the surface is extremely poor and the aluminum filmtends to peel off when bended.

As the results of the inventors intensive research to overcome saiddrawbacks, it has been found that said drawbacks can completely beeliminated.

One object of this invention is that a substrate covered with aluminumis heat treated at a temperature of not lower than 400C, but below themelting point of aluminum in an inert atmosphere and thereafter the thustreated substrate is taken out into the air Another object is that asubstrate covered with aluminum is contacted with a very small amount ofa surface treating agent selected from active hydrogencontainingcompounds, oxygen and halogens, then is heat treated at a temperature ofnot lower than 400 C, but below the melting point of aluminum in aninert atmosphere and thereafter is taken out into the air or that asubstrate covered with aluminum is heat treated at a temperature of notlower than 400 C, but below the melting point of aluminum, then iscontacted with a very small amount of a surface treating agent selectedfrom active hydrogen-containing compound, oxygen and halogen andthereafter is taken out into theair.

According to the method of this invention, the aluminum film which hasno cracks and pin-holes on its surface, has uniform thickness, exhibitsexcellent surface luster and is bonded strongly to the substrate and isnot peeled off therefrom can be obtained.

Other objects will be apparent from the description hereinafter.

Alkyl aluminum compounds used in this invention include any alkylaluminu compounds capable of depositing aluminum by thermaldecomposition. Among them, the following are preferable because they areeasily thermally decomposed and are economical. That is, dialkylaluminum hydride or trialkyl aluminum having alkyl groups of two 20carbon atoms such as triethyl aluminum, diethyl aluminum hydride,trinormal propyl aluminum, triisopropyl aluminum, trinormalbutylaluminum, dinorrnalbutyl aluminum hydride, triisobutyl aluminum,diisobutyl aluminum hydride, trinormalbenzyl aluminum, trinormalhexylaluminum, trinormaloctyl aluminum, tri-2-ethylhexyl aluminum, di-2-ethylhexyl aluminum hydride, and tridecyl aluminum, or mixtures thereof.

Furthermore, the alkyl aluminum compound may be used together with acompound capable of producing a complex compound with the alkyl aluminumcompound such as an alkali metal compound, an ether, a tertiary amine, aquaternary ammonium salt, etc., which are mentioned in U.S. Pat. Nos.3,154,407 and 3,273,996 to attain plating of aluminum in high purity. Inaddition, the alkyl aluminum compound may beused in admixture with aninert organic solvent such as hexane, heptane, octane, cyclopentane,cyclohexane, benzene, toluene, xylene, petroleum, paraffins, alkylbenzene, diphenyl, etc.

Substrates to be plated include, for example, metals such as iron,steel, aluminum, copper, brass pottery, glass, organic and inorganicresins, etc.

The substrate is preferably cleaned prior to plating.

The substrate is heated to a temperature higher than thermaldecomposition temperature of alkyl aluminum compound, preferably of 300600 C and is contacted with plating solution or plating vapor. Thesubstrate may be heated by known heating methods and e.g., resistanceheating, induction heating, etc., may be employed depending upon kind orshape of the substrate. The induction heating is preferable forcontinuous heating of especially thin metal sheet.

As the method for obtaining a substrate covered with aluminum accordingto this invention, either one of the method according to which a heatedsubstrate is contacted with a liquid alkyl aluminum compound and themethod according to which a heated substrate is contacted with vapor ofan alkyl aluminum compound may be used. Election of either one of thesemethods depends upon kind and shape of the substrate to be plated. Thesubstrate may be covered with aluminum by thermal decomposition of analkyl aluminum compound on a substrate by one time heating or byintermittent two or more heatings. The latter is especially preferable.Further, there is the case that the latter method does not necessitateheat-treating of a substrate covered with aluminum.

The thermal decomposition may be carried out in the presence of acompound capable: of accelerating the thermal decomposition such astitanium chloride, titanium bromide, vanadium chloride, iron chloride,copper chloride, etc. which are mentioned in U.S. Pat. No. 3,306,732.Addition of said compound is useful especially for plating a substrateof low heat stability.

The thermal decomposition is required to be carried out in an inertatmosphere, but no critical limitation is present in pressure foroperation.

The substrate covered with aluminum as mentioned above is then fed to aheat treatment step or is firstly contacted with a very small amount ofa surface treating agent selected from the group consisting of activehydrogen-containing compounds, oxygen and halogen, and thereafter fed tothe heat treatment step. The heat treatment in this invention is carriedout by heating and keeping the substrate at a temperature of not lowerthan 400 C, but below the melting point of aluminum, preferably of 450600 C.

When the heat treating temperature is lower than 400 C, good surfaceproperties cannot be obtained and furthermore a long period of time isrequired for heat treatment. For example, with a substrate of iron, areaction occurs between iron and aluminum and the aluminum film is aptto peel off.

In this invention, the aluminum heat treatment is effected in thepresence of an inert gas or a molten salt. Usually, nitrogen, argon andhelium are effectively used, but it should be noted that this inventionis not limited to the use thereof.

The heat treating time somewhat varies depending upon kind and shape ofthe substrate, thickness of aluminum film and heating temperature, butgenerally is seconds 30 minutes. However, with a substrate of iron, toolong treating time causes a reaction between aluminum and iron todeteriorate the plate surface and hence industrially, the substrate ispreferably kept for 20 seconds minutes.

After completion of the heat treatment, the substrate is taken out intothe air or firstly is contacted with a small amount of a surfacetreating agent selected from the group consisting of activehydrogen-containing compound, oxygen and halogen and thereafter takenout into the air.

The contact of the substrate with a surface treating selected from theactive hydrogen-containing compound, oxygen and halogen may be carriedout before said heat treatment. As mentioned above, the contact of thesubstrate with a very small amount of a surface treating agent selectedfrom active hydrogencontaining compound, oxygen and halogen before orafter the heat treatment results in more excellent aluminum plating thanthat attained only by heat treatment.

Illustrative of the active hydrogen-containing compounds to be contactedwith the substrate covered with aluminum are compounds containing atleast one substitutable hydrogen such as water, ammonia primary orsecondary amine compounds, e.g., dimethyl amine, monobutyl amine, etc.;sulfides, e.g., hydrogen sulfide, ethyl thioalcohol, dodecylthioalcohol, etc.; monoor poly-hydric alcohols, e.g., methanol, ethanol,isopropylalcohol, butanol, ethylene glycol, propylene glycol, glycerine,etc.; carboxylic acids, e.g., acetic acid, naphthenic acid, stearicacid, adipic acid, maleic acid, phthalic acid, etc.; and inorganicacids, e.g., hydrogen chloride, hydrogen fluoride, hydrogen bromide,nitric acid, etc.

Those active hydrogen-containing compounds are used as a solution whichcontains 10 10,000 ppm, preferably 100 1,000 ppm (weight basis) of saidcompound dissolved in aromatic hydrocarbons such as benzene, toluene,xylene, naphthalene, alkyl benzene, etc., aliphatic hydrocarbons such aspentane, hexane, octane, decene, etc., and mixtures thereof or as anatmosphere of the active hydrogen-containing compound of 0.1 mmHg,preferably 0.1 10 mml-lg.

In case of treatment with oxygen, the substrate is contacted with saidaromatic or aliphatic hydrocarbon containing 10 10,000 ppm, preferably100 1,000 ppm (weight basis) of oxygen or is used as an oxygenatmosphere of 0.01 100 mmHg, preferably 0.1 80 mml-lg.

Furthermore, when halogens such as fluorine, chlorine, bromine, etc. areused, they are used as a halogen atmosphere of 0.01 20 mmHg, preferably0.1 10

mmHg or as a solution containing 10 2,000 ppm of a halogen dissolved ina suitable solvent such as a paraffin. When the halogen is contacted ina vapor phase, the vapor alone is not contacted, but the vapor isdiluted with an inert gas and the treatment is carried out under normalpressure or higher pressure.

Said treatment is carried out at 0 300 C, preferably 15 200 C.

As mentioned above, the method of this invention provides the followingadvantages as compared with the conventional method in which thesubstrate covered with aluminum is taken out without further treatments.

That is, the aluminum film on the substrate has no cracks and pin-holeson its surface, has a uniform thickness, exhibits excellent surfaceluster and is bonded strongly to the substrate.

The substrate plated with aluminum in accordance with this invention hashigh corrosion resistance and oxidation resistance at a high temperatureand excellent electric characteristics. Furthermore, the substrateplated can be subjected to metal surface treatment, such as knownsealing treatment, stabilizaton treatment and alumite finishing. Due tothese excellent characteristics the industrial value of this inventionis extremely great.

The following Examples are given by way of specifically illustratingthis invention and are not intended to be construed as limiting in anycase.

EXAMPLE 1 A steel sheet of 50 mm X 50 mm X 0.6 mm was washed with waterand subsequently with alcohols and then dried. Thus treated steel sheetwas used as a specimen.

The whole process steps from the heat treatment of the specimen untiltaking out it into the air were carried out in argon atmosphere.

Said specimen was heated to 400 C in argon atmosphere and thereafter wasdipped in 500 cc of an alkyl aluminum solution which comprises 81percent by weight of diisobutyl aluminum hydride, 11 percent by weightof diethyl aluminum hydride, 5 percent by weight of triisobutylaluminum, and 3 percent by weightpf triethyl aluminum at 20 C.

After lapse of one minute, the specimen was withdrawn from the solutionand deposited alkyl aluminum was maintained in argon atmosphere at C andwashed away.

Furthermore, the same procedure as mentioned above was repeated oncemore to effect aluminum plating. Subsequently, the specimen thus platedwith aluminum was heated to 450 C in argon atmosphere. After thespecimen was kept at that temperature for 5 minutes, it was cooled toroom temperature in argon gas and then taken out into the air.

Thus obtained substrate plated with aluminum has a film of 1.1 p. inthickness and has excellent luster of silver white.

Furthermore, an acid resistance test was made by dipping in 500 cc of 25weight percent aqueous nitric acid solution at 20 C said platedsubstrate which was covered by solid paraffin in a width of 10 mm aroundsaid substrate.

Even after lapse of 30 minutes, no bubbles were generated and no changewas observed in the plate surface.

For comparison, the same another specimen which was plated with aluminumin the same manner as mentioned above was taken out into the air withoutheat treatment.

Thus obtained substrate plated with aluminum has a film of 1.1 p. inthickness and its surface showed silver white. The same acid resistancetest was made with this substrate. After lapse of 11 minutes, bubbleswere generated and after lapse of 20 minutes the aluminum film on thesubstrate was nearly peeled off.

From the foregoing results, it will be seen that with the substratesplated with aluminum in the same thickness, the properties of thesurface subjected to the heat treatment was extremely superior to thoseof the surface subjected to no heat treatment.

EXAMPLE 2 The same specimen as in Example 1 and which was cleaned in thesame manner as in Example 1 was employed in this Example. The treatmentwas carried out in argon atmosphere as in Example I. The specimen waspre-heated to 500C and was dipped in an alkyl aluminum solution havingthe same compositions as in Example 1, heated to 200 C.

After lapse of one minute, the specimen was withdrawn and washed with500 cc of hexane.

Then, the specimen was heated to 500 C in argon atmosphere and kept atthat temperature for 5 minutes. Thereafter, it was cooled and taken outinto the air. The steel sheet thus plated with aluminum had excellentluster of silver white and had'excellent surface properties. The averagethickness of the aluminum film was 2.1 .u. determined by weightincreased.

The specimen was also subjected to the acid resistance test in the samemanner as in Example 1. Even after lapse of 30 minutes, no bubbles weregenerated.

For comparison, the specimen prior to said heat treatment was cooled inargon and then taken out into the air.

The steel sheet thus plated with aluminum had a grey color and littleluster. The same acid resistance test as mentioned above was given tothe specimen. After lapse of 5 minutes, generation of bubbles wasobserved.

For further comparison, instead of said heat treatment, the specimen wassimilarly heated to 300 C in argon atmosphere and kept at thattemperature for 5 minutes. Then, it was cooled in argon and taken outinto the air. Thus obtained steel sheet plated with aluminumshowed greycolor and had little luster. The specimen was subjected to the same acidresistance test as mentioned above. After lapse of 7 minutes, generationof bubbles was observed.

From the above results, it will be seen that with the steel sheetsplated with aluminum in the same thickness, the luster and properties ofthe surface treated according to this invention were superior to thoseof the surface which was not treated in accordance with this invention.

EXAMPLE 3 A substrate covered with aluminum treated in the same manneras in Example 1 until the heat treatment step was contacted with 500 ccof hexane containing 0.01 percent by weight of water at 20 C for oneminute and then taken out into the air.

Thus obtained steel sheet plated with aluminum showed excellent lusterof silver white and had extremely excellent surface properties.

Said steel sheet was subjected to the same acid resistance test as inExample 1. Even after lapse of 50 minutes, generation of bubbles was notobserved.

In said method, instead of water treatment, the steel sheets weretreated with 500 cc of hexane containing 0.01 percent by weight ofethanol, 500 cc of hexane containing 0.01 percent by weight of oxygenand argon atmosphere containing chlorine gas of 1 mmHg, respectively andthey were taken out into the air. Thus obtained steel sheets plated withaluminum showed excellent luster of silver white and had extremelyexcellent surface properties.

. Each steel sheet was subjected to the same acid resistance test as inExample 1. The same results as in case of the water treatment wereobtained.

EXAMPLE 4 A substrate covered with aluminum in the same manner as inExample 1 was contacted with 500 cc of hexane containing 0.01 percent byweight of water at 20 C for one minute. Thereafter, it was heated to 500C in argon atmosphere for 5 minutes and kept at that temperature. Then,the substrate was cooled to room temperature in argon gas and taken outinto the air. Thus obtained steel sheet plated with aluminum showedexcellent luster of silver white and had extremely excellent surfaceproperties.

This steel sheet was subjected to the same acid resistance test as inExample I to find no generation of bubbles even after lapse of 40minutes.

In said method, instead of the water treatment, steel sheets weretreated with 500 cc of hexane containing 0.01 percent by weight ofethanol, 500 cc of hexane containing 0.01 percent by weight of oxygenand argon atmosphere containing chlorine gas of 1 mmHg, respectively.Thereafter, they were heat treated as mentioned above, cooled and thentaken out into the air. They had excellent surface properties as in thecase of the water treatment.

Each steel sheet thus treated was subjected to the acid resistance testas in Examplel to obtain the same results as in case of the watertreatment.

What is claimed is: it

1. In a method for aluminum plating of a substrate by contacting aheated substrate with an alkyl aluminum compound to cause thermaldecomposition of said alkyl aluminum compound, an improvement whichcomprises heat treating said substrate covered with aluminum at atemperature of not lower than 400 C, but below the melting point ofaluminum for 10 seconds 30 minutes in an inert atmosphere, thencontacting thus treated substrate with a small amount of a surfacetreating agent selected from active hydrogencontaining compound, oxygenand halogen, and thereafter taking out the substrate into the air.

2. A substrate plated with aluminum according to the method as claimedin claim 1.

3. A method according to claim. 1, wherein the alkyl aluminum compoundis selected from dialkyl aluminum hydride, trialkyl aluminum havingalkyl groups of two-20 carbon atoms and a mixture thereof.

4. A method according to claim 1, wherein the substrate heated to300-600 C. was contacted with liquid or vapor of the alkyl aluminumcompound to plate the substrate with aluminum.

5. A method according to claim 1, wherein the heat treatment was carriedout at 450-600 C. for 20 seconds 15 minutes.

6. A method according to claim 1, wherein the active-hydrogen containingcompound is selected from the group consisting of water, ammonia,primary and secondary amine compounds, sulfides, monoand polyhydricalcohols, carboxylic acids, and inorganic acids.

7. A method according to claim 6, wherein the primary and secondaryamine compounds are selected from the group consisting of dimethylamine, and monobutyl amine.

8. A method according to claim 6, wherein the sultide is selected fromthe group consisting of hydrogen sulfide, ethyl thioalcohol, dodecylthioalcohol.

9. A method according to claim 6, wherein the monoand poly-hydricalcohols are methanol, ethanol, isopropyl-alcohol, butanol, ethyleneglycol, propylene glycol and glycerine.

10. A method according to claim 6, wherein the carboxylic acid isselected from the group consisting of acetic acid, naphthenic acid,stearic acid, adipic acid, maleic acid and phthalic acid.

1 l. A method according to claim 6, wherein the inorganic acid isselected from the group consisting of hydrogen chloride, hydrogenfluoride, hydrogen bromide and nitric acid.

12. A method according to claim 1, wherein the halogen is selected fromchlroine, fluorine and bromine.

13. A method according to claim 1, wherein the substrate plated withaluminum is contacted with a solution containing activehydrogen-containing compound in an amount of 10 10,000 ppm.

14. A method according to claim 1, wherein the substrate plated withaluminum is contacted with an atmosphere of active hydrogen-containingcompound of 0.01 20 mmHg.

15. A method according to claim 1, wherein the substrate plated withaluminum is contacted with a solution containing 10 10,000 ppm ofoxygen.

16. A method according to claim 1, wherein the substrate plated withaluminum is contacted with a gas atmosphere containing oxygen of 0.01100 mmHg.

17. A method according to claim I, wherein the substrate plated withaluminum is contacted with a solution containing 10 2,000 ppm of ahalogen.

18. A method according to claim 1, wherein the substrate plated withaluminum is contacted with a gas atmosphere containing a halogen of 0.0120 mmHg.

19. A method according to claim 6, wherein the substrate plated withaluminum is contacted with the surface active agent at 300 C.

20. In a method for aluminum plating a substrate by contacting a heatsubstrate with an alkyl aluminum compound to cause thermal decompositionof said alkyl aluminum compound, an improvement which comprisescontacting said substrate covered with aluminum with a small amount of asurface treating agent selected from active hydrogen-containingcompound, oxygen and halogens, then heat treating the substrate at atemperature of not lower than 400 C, but below the melting point ofaluminum for seconds 30 minutes and thereafter taking out thus treatedsubstrate into the air.

21. A method according to claim 20, wherein the alkyl aluminum compoundis selected from dialkyl aluminum hydride, trialkyl aluminum havingalkyl groups of two-20 carbon atoms and a mixture thereof.

22. A method according to claim 20, wherein the substrate heated to300-600 C. was contacted with liquid or vapor of the alkyl aluminumcompound to plate the substrate with aluminum.

23. A method according to claim 20, wherein the heat treatment wascarried out at 450-600 C. for 20 seconds 15 minutes.

24. A method according to claim 20, wherein the active-hydrogencontaining compound is selected from the group consisting of water,ammonia, primary and secondary amine compounds, sulfides, monoandpolyhydric alcohols, carboxylic acids, and inorganic acids.

25. A method according to claim 24, wherein the primary and secondaryamine compounds are selected from the group consisting of dimethylamine, and monobutyl amine.

26. A method according to claim 24, wherein the sultide is selected fromthe group consisting of hydrogen sulfide, ethyl thioalcohol, dodecylthioalcohol.

27. A method according to claim 24, wherein the monoand poly-hydricalcohols are methanol, ethanol, isopropyl-alcohol, butanol, ethyleneglycol, propylene glycol and glycerine.

28. A method according to claim 24, whrein the carobxylic acid isselected from the group consisting of acetic acid, naphthenic acid,stearic acid, adipic acid, maleic acid and phthalic acid.

29. A method according to claim 1, wherein the inorganic acid isselected from the group consisting of hydrogen chloride, hydrogenfluoride, hydrogen bromide and nitric acid.

30. A method according to claim 20, wherein the halogen is selected fromchlorine, fluorine and bromine. 1

31. A method according to claim 30, wherein the substrate plated withaluminum is contacted with a solution containing activehydrogen-containing compound in an amount of 10 10,000 ppm.

32. A method accoding to claim 20, wherein the substrate plated withaluminum is contacted with an atmosphere of active hydrogen-containingcompound of 0.01 20 mmHg.

33. A method according to claim'20, wherein the substrate plated withaluminum is contacted with a solution containing 10 10,000 ppm ofoxygen.

34. A method according to claim 20, wherein the substrate plated withaluminum is contacted with a gas atmosphere containing oxygen of 0.01mmHg.

35. A method according to claim 20, wherein the substrate plated withaluminum is contacted with a solution containing 10 2,000 ppm ofhalogen.

36. A method according to claim 30, wherein the substrate plated withaluminum is contacted with a gas atmosphere containing a halogen of 0.0120 mmHg.

37. A method according to claim 20, wherein the substrate plated withaluminum is contacted with the surface active agent at 0 300 C.

38. A substrate plated with aluminum according to the method as claimedin claim 20.

t t 1 =8 i

2. A substrate plated with aluminum according to the method as claimedin claim
 1. 3. A method according to claim 1, wherein the alkyl aluminumcompound is selected from dialkyl aluminum hydride, trialkyl aluminumhaving alkyl groups of two-20 carbon atoms and a mixture thereof.
 4. Amethod according to claim 1, wherein the substrate heated to 300*-600*C. was contacted with liquid or vapor of the alkyl aluminum compound toplate the substrate with aluminum.
 5. A method according to claim 1,wherein the heat treatment was carried out at 450*-600* C. for 20seconds - 15 minutes.
 6. A method according to claim 1, wherein theactive-hydrogen containing compound is selected from the groupconsisting of water, ammonia, primary and secondary amine compounds,sulfides, mono- and poly-hydric alcohols, carboxylic acids, andinorganic acids.
 7. A method according to claim 6, wherein the primaryand secondary amine compounds are selected from the group consisting ofdimethyl amine, and monobutyl amine.
 8. A method according to claim 6,wherein the sulfide is selected from the group consisting of hydrogensulfide, ethyl thioalcohol, dodecyl thioalcohol.
 9. A method accordingto claim 6, wherein the mono- and poly-hydric alcohols are methanol,ethanol, isopropyl-alcohol, butanol, ethylene glycol, propylene glycoland glycerine.
 10. A method according to claim 6, wherein the carboxylicacid is selected from the group consisting of acetic acid, naphthenicacid, stearic acid, adipic acid, maleic acid and phthalic acid.
 11. Amethod according to claim 6, wherein the inorganic acid is selected fromthe group consisting of hydrogen chloride, hydrogen fluoride, hydrogenbromide and nitric acid.
 12. A method according to claim 1, wherein thehalogen is selected from chlroine, fluorine and bromine.
 13. A methodaccording to claim 1, wherein the substrate plated with aluminum iscontacted with a solution containing active hydrogen-containing compoundin an amount of 10 - 10,000 ppm.
 14. A method according to claim 1,wherein the substrate plated with aluminum is contacted with anatmosphere of active hydrogen-containing compound of 0.01 - 20 mmHg. 15.A method according to claim 1, wherein the substrate plated withaluminum is contacted with a solution containing 10 - 10,000 ppm ofoxygen.
 16. A method according to claim 1, wherein the substrate platedwith aluminum is contacted with a gas atmosphere containing oxygen of0.01 - 100 mmHg.
 17. A method according to claim 1, wherein thesubstrate plated with aluminum is contacted with a solution containing10 - 2,000 ppm of a halogen.
 18. A method according to claim 1, whereinthe substrate plated with alUminum is contacted with a gas atmospherecontaining a halogen of 0.01 - 20 mmHg.
 19. A method according to claim6, wherein the substrate plated with aluminum is contacted with thesurface active agent at 0* -300* C.
 20. In a method for aluminum platinga substrate by contacting a heat substrate with an alkyl aluminumcompound to cause thermal decomposition of said alkyl aluminum compound,an improvement which comprises contacting said substrate covered withaluminum with a small amount of a surface treating agent selected fromactive hydrogen-containing compound, oxygen and halogens, then heattreating the substrate at a temperature of not lower than 400* C, butbelow the melting point of aluminum for 10 seconds -30 minutes andthereafter taking out thus treated substrate into the air.
 21. A methodaccording to claim 20, wherein the alkyl aluminum compound is selectedfrom dialkyl aluminum hydride, trialkyl aluminum having alkyl groups oftwo-20 carbon atoms and a mixture thereof.
 22. A method according toclaim 20, wherein the substrate heated to 300*-600* C. was contactedwith liquid or vapor of the alkyl aluminum compound to plate thesubstrate with aluminum.
 23. A method according to claim 20, wherein theheat treatment was carried out at 450*-600* C. for 20 seconds - 15minutes.
 24. A method according to claim 20, wherein the active-hydrogencontaining compound is selected from the group consisting of water,ammonia, primary and secondary amine compounds, sulfides, mono- andpoly-hydric alcohols, carboxylic acids, and inorganic acids.
 25. Amethod according to claim 24, wherein the primary and secondary aminecompounds are selected from the group consisting of dimethyl amine, andmonobutyl amine.
 26. A method according to claim 24, wherein the sulfideis selected from the group consisting of hydrogen sulfide, ethylthioalcohol, dodecyl thioalcohol.
 27. A method according to claim 24,wherein the mono- and poly-hydric alcohols are methanol, ethanol,isopropyl-alcohol, butanol, ethylene glycol, propylene glycol andglycerine.
 28. A method according to claim 24, whrein the carobxylicacid is selected from the group consisting of acetic acid, naphthenicacid, stearic acid, adipic acid, maleic acid and phthalic acid.
 29. Amethod according to claim 1, wherein the inorganic acid is selected fromthe group consisting of hydrogen chloride, hydrogen fluoride, hydrogenbromide and nitric acid.
 30. A method according to claim 20, wherein thehalogen is selected from chlorine, fluorine and bromine.
 31. A methodaccording to claim 30, wherein the substrate plated with aluminum iscontacted with a solution containing active hydrogen-containing compoundin an amount of 10 - 10,000 ppm.
 32. A method accoding to claim 20,wherein the substrate plated with aluminum is contacted with anatmosphere of active hydrogen-containing compound of 0.01 - 20 mmHg. 33.A method according to claim 20, wherein the substrate plated withaluminum is contacted with a solution containing 10 - 10,000 ppm ofoxygen.
 34. A method according to claim 20, wherein the substrate platedwith aluminum is contacted with a gas atmosphere containing oxygen of0.01 - 100 mmHg.
 35. A method according to claim 20, wherein thesubstrate plated with aluminum is contacted with a solution containing10 - 2,000 ppm of halogen.
 36. A method according to claim 30, whereinthe substrate plated with aluminum is contacted with a gas atmospherecontaining a halogen of 0.01 - 20 mmHg.
 37. A method according to claim20, wherein the substrate plated with aluminum is contacted with thesurface active agent at 0* -300* C.
 38. A substrate plated with aluminumaccording to the method as claimed in claim 20.